1. Field of the Disclosure
The present invention is directed to thin film capacitors, and to multilayer interconnect structures with embedded thin film capacitors.
2. Description of the Related Art
An established method of fabricating electronic substrates and interconnects is by electroplating metal layers and metal interconnects and embedding these in a polymer based dielectric. One fabrication technique uses drill & fill to provide conductive vias.
An alternative solution that overcomes many of the inherent disadvantages of the drill & fill approach, is to fabricate vias by depositing copper or other metal into a pattern created in a photo-resist, using a technology otherwise known as ‘pattern plating’.
In pattern plating, a seed layer is first deposited over a substrate, providing a conducting layer onto which copper may be deposited. Then a layer of photo-resist is deposited thereover and subsequently exposed to create a pattern, and selectively removed to make trenches that expose the seed layer. Via posts are created by depositing copper into the photo-resist trenches. The remaining photo-resist is then removed, the seed layer is etched away, and a dielectric material, that is typically a polymer impregnated glass fiber mat, is laminated thereover and therearound to encase the vias posts. Various techniques and processes can then be used to planarize the dielectric material, removing part of it to expose the tops of the via posts to allow conductive connection to ground thereby, for building up the next metal layer thereupon. Subsequent layers of metal conductors and via posts may be deposited there onto by repeating the process to build up a desired multilayer structure.
In an alternative but closely linked technology, known hereinafter as ‘panel plating’, a continuous layer of metal or alloy is deposited onto a substrate. A layer of photo-resist is deposited on top of the substrate, and a pattern is developed therein. The pattern of developed photo-resist is stripped away, selectively exposing the metal thereunder, which may then be etched away. The undeveloped photo-resist protects the underlying metal from being etched away, and leaves a pattern of upstanding features and vias.
After stripping away the undeveloped photo-resist, a dielectric material, such as a polymer impregnated glass fiber mat, may be laminated around and over the upstanding copper features and/or via posts. After planarizing, subsequent layers of metal conductors and via posts may be deposited there onto by repeating the process to build up a desired multilayer structure.
The via layers created by pattern plating or panel plating methodologies described above are typically known as ‘via posts’ and feature layers from copper.
It will be appreciated that the general thrust of the microelectronic evolution is directed towards fabricating ever smaller, thinner, lighter and more powerful products having high reliability. The use of thick cored interconnects prevents ultra-thin products being attainable. To create ever higher densities of structures in the interconnect IC substrate or ‘interposer’, ever more layers of ever smaller connections are required. Indeed, sometimes it is desirable to stack components on top of each other.
If plated, laminated structures are deposited on a copper or other appropriate sacrificial substrate, the substrate may be etched away leaving free standing, coreless laminar structures. Further layers may be deposited on the side previously adhered to the sacrificial substrate, thereby enabling a two sided build up, which minimizes warping and aids the attaining of planarity.
One flexible technology for fabricating high density interconnects is to build up pattern or panel plated multilayer structures consisting of metal vias or features in a dielectric matrix. The metal may be copper and the dielectric may be a fiber reinforced polymer. Typically a polymer with a high glass transition temperature (Tg) is used, such as polyimide, for example. These interconnects may be cored or coreless, and may include cavities for stacking components. They may have odd or even numbers of layers. Enabling technology is described in previous patents issued to Amitec-Advanced Multilayer Interconnect Technologies Ltd.
For example, U.S. Pat. No. 7,682,972 to Hurwitz et al. titled “Advanced multilayer coreless support structures and method for their fabrication” describes a method of fabricating a free standing membrane including a via array in a dielectric, for use as a precursor in the construction of superior electronic support structures, includes the steps of fabricating a membrane of conductive vias in a dielectric surround on a sacrificial carrier, and detaching the membrane from the sacrificial carrier to form a free standing laminated array. An electronic substrate based on such a free standing membrane may be formed by thinning and planarizing the laminated array, followed by terminating the vias. This publication is incorporated herein by reference in its entirety.
U.S. Pat. No. 7,669,320 to Hurwitz et al. titled “Coreless cavity substrates for chip packaging and their fabrication” describes a method for fabricating an IC support for supporting a first IC die connected in series with a second IC die; the IC support comprising a stack of alternating layers of copper features and vias in insulating surround, the first IC die being bondable onto the IC support, and the second IC die being bondable within a cavity inside the IC support, wherein the cavity is formed by etching away a copper base and selectively etching away built up copper. This publication is incorporated herein by reference in its entirety.
U.S. Pat. No. 7,635,641 to Hurwitz et al. titled “integrated circuit support structures and their fabrication” describes a method of fabricating an electronic substrate comprising the steps of; (A) selecting a first base layer; (B) depositing a first etchant resistant barrier layer onto the first base layer; (C) building up a first half stack of alternating conductive layers and insulating layers, the conductive layers being interconnected by vias through the insulating layers; (D) applying a second base layer onto the first half stack; (E) applying a protective coating of photo-resist to the second base layer; (F) etching away the first base layer; (G) removing the protective coating of photo-resist; (H) removing the first etchant resistant barrier layer; (I) building up a second half stack of alternating conductive layers and insulating layers, the conductive layers being interconnected by vias through the insulating layers, wherein the second half stack has a substantially symmetrical lay up to the first half stack; (J) applying an insulating layer onto the second hall stack of alternating conductive layers and insulating layers, (K) removing the second base layer, and (L) terminating the substrate by exposing ends of vias on outer surfaces of the stack and applying terminations thereto. This publication is incorporated herein by reference in its entirety.
RF (Radio Frequency) technologies, such as Bluetooth, Wi-Fi and the like, are becoming widely implemented in various devices, including mobile phones and automobiles.
In addition to processing and memory chips, RF devices in particular, require passive components such as capacitors and filters of various sorts. Such passive components may be surface mounted, but to enable ever greater miniaturization and cost savings, such devices may be embedded within the substrates.
One advantage of the plating process for via fabrication is that shaped vias may be deposited instead of simple cylindrical posts. This provides some flexibility in the fabrication of capacitors, which can be embedded in the substrates themselves, or separately fabricated and then surface mounted onto a substrate.
Embedding passive devices within substrates is not without its downside. The more complicated the substrate, the higher the likelihood of some aspect failing, and so embedding components can adversely affect yields. The more complicated and integrated a component, the more difficult it is to isolate a root cause of some failure thereof and to attend to the underlying causes.
Aspects of the present invention are directed to substrates with embedded passive components and methods of fabrication thereof.